lavc/h264_ps: always include the stop bit in [s|p]ps->data

The VideoToolbox hwaccel needs the entire NAL (including the stop bit),
but ff_h2645_packet_split may remove it. Detect this case by looking for
bit counts divisible by 8 and insert a stop-bit-only 0x80 byte.

Signed-off-by: rcombs <rcombs@rcombs.me>

libavcodec/h264_ps.c

@@ -351,6 +351,10 @@ int ff_h264_decode_seq_parameter_set(GetBitContext *gb, AVCodecContext *avctx,
     }
     memcpy(sps->data, gb->buffer, sps->data_size);
 
+    // Re-add the removed stop bit (may be used by hwaccels).
+    if (!(gb->size_in_bits & 7) && sps->data_size < sizeof(sps->data))
+        sps->data[sps->data_size++] = 0x80;
+
     profile_idc           = get_bits(gb, 8);
     constraint_set_flags |= get_bits1(gb) << 0;   // constraint_set0_flag
     constraint_set_flags |= get_bits1(gb) << 1;   // constraint_set1_flag
@@ -775,6 +779,10 @@ int ff_h264_decode_picture_parameter_set(GetBitContext *gb, AVCodecContext *avct
     }
     memcpy(pps->data, gb->buffer, pps->data_size);
 
+    // Re-add the removed stop bit (may be used by hwaccels).
+    if (!(bit_length & 7) && pps->data_size < sizeof(pps->data))
+        pps->data[pps->data_size++] = 0x80;
+
     pps->sps_id = get_ue_golomb_31(gb);
     if ((unsigned)pps->sps_id >= MAX_SPS_COUNT ||
         !ps->sps_list[pps->sps_id]) {